Percussive welder

ABSTRACT

One of two small workpieces that are to be welded together is slidingly mounted in a fixed workholder and the other is firmly gripped by a movable workholder. To carry out an operating cycle, the movable workholder is reciprocated by two lobes of a cam that makes one revolution when momentarily connected to a relatively large mass that rotates at constant velocity. Initially the first slidable workpiece is placed at random at a position that is advanced slightly from the position desired for the welding operation but the first reciprocation of the second workpiece is against the slidable workpiece to retract it precisely to the desired position for a welding operation. In carrying out the second reciprocation, the two workpieces are charged by capacitance and as the gap between the two workpieces narrows a high frequency pulse triggers an arc between the two workpieces and the continued advance of the second workpiece crowds the two workpieces together for final fusion.

United States Patent [15] 3,654,423 Phillips et al. [4 Apr. 4, 1972 [54]PERCUSSIVE WELDER Primary Examiner-R. F. Staubly [72] inventors: DelbertL. Phillips, 4 Malibu Cove Colony, Attorney'smytm Roston & Pavm Malibu,Calif. 90265; Lewis Clark Feightner, 19800 Lassen St., Chatsworth,Calif. 91311 [5 7] ABSTRACT One of two small workpieces that are to bewelded together is slidingly mounted in a fixed workholder and the otheris firmly [22] Filed. June 1, 1970 gripped by a movable workholder. Tocarry out an operating PP 54,074 cycle, the movable workholder isreciprocated by two lobes of a cam that makes one revolution whenmomentarily con- Related Application Dam nected to a relatively largemass that rotates at constant [62] Division of Ser. No. 715,773, Mar.25, 1968. velocity. Initially the first slidable workpiece is placed atrandom at a position that is advanced slightly from the position 314/34desired for the welding operation but the first reciprocation of [51] Cl9/22 523k 9/06,}105" 31/30 the second workpiece is against the slidableworkpiece to [58] Field of Search ..219/95, 96, 135; 314/34 it preciselyto the desired position f a wglding tion. n carrying out the secondreciprocation, t e two wor [56] References Cited pieces are charged bycapacitance and as the gap between the UNITED STATES PATENTS twoworkpieces narrows a high frequency pulse triggers an arc between thetwo workpieces and the continued advance of the 3,254,193 5/ 1966Phillips -219/95 second workpiece crowds the two workpieces together for3,254,194 5/1966 Phillips ..219 95 fi al f i 3,254,195 5/1966 Phillipset al. ..219/96 5 Claims, 12 Drawing Figures d /e Zaw/Vg/faye M4 if;11,4554, 5

Va/qfie I 785; 4 0/ 2 7/ If? ifs #4776 I ere 5/ flea/9772f PATENTEDAPR 4I972 3, 654,423

SHEET 2 BF 4 fax/rte PERCUSSIVE WELDER CROSS-REFERENCE TO RELATEDAPPLICATIONS This is a division of application Ser. No. 715,773, filedMar. 25, 1968.

BACKGROUND OF THE INVENTION The invention relates to an arc weldingtechnique of the character disclosed in the three Phillips U.S. Pat.Nos. 3,254,193, 3,254,194 and 3,254,195 and it is to be understood stoodthat any of the circuits disclosed in the three prior patents may beadapted for use in the present disclosure even through the circuitdisclosed herein and has a special utility. All three of these patentsteach that with an electrode spaced from a workpiece or with twoworkpieces spaced from each other by a suitable gap, an arc may becreated across the gap by first employing capacitor means to create apotential across the gap and then employing a high frequency pulse totrigger an arc.

The present invention is directed primarily to the problem of developinga means and a method of joining small workpieces by arc welding inhighly accurately repeated operating cycles wherein the'requiredduration of the arc may be as low as one third of a millisecond andusually does not exceed 8 milliseconds. The basic problem is to provideexceedingly accurate and unvarying control on such a small time scale.

The Phillips U.S. Pat. No. 3,254,193 is of special interest in that itteaches mounting one of the two workpieces on a fixed workholder,mounting the other workpiece on a relatively light workholder and thenapplying force to the workholder to accelerate it to high velocity tobring the two workpieces together with the arc triggered as the gapnarrows between the two workpieces. The movable workholder is normallyretracted by a suitable spring and is electromagnetically advanced byenergization of coil means to carry out an operating cycle. Thisprocedure is operative for its purpose but has certain disadvantageswhen the primary requirement is accurate adjustability and accuraterepetition of operating cycles and especially so when the duration ofthe arc must be controlled within microseconds and the operating cyclemust be repeated rapidly for high speed production.

The described prior art procedure has the following disadvantages:

1. Friction is a variable factor and the presence of a foreign particlemay change both the rate of movement of the workholder and the timing ofthe arc relative thereto.

2. Since the advance of the workholder to carry out an operating cycleis increasingly opposed by the return spring, the spring is a variablefactor.

. The electromagnetic driving force increases exponentially at one ratewhile the opposing resistance of the spring increases at a differentrate to make close adjustment difficult.

4. Each operating cycle necessarily includes time for acceleration ofthe workholder as a free body prior to the actual welding operation andfor reasons including the above factors the rate and degree ofacceleration of the free body is not subject to the degree of controlrequired for accurate repetition of an operating cycle.

5. The triggering of the arc is responsive to changes that occur in thecurrent flow in the circuitry that includes the coil for actuating theworkholder and largely because of the heretofore stated factors thetiming of the triggering of the arc may vary from cycle to cyclerelative to the position of the moving iron core.

6. The extent to which the two workpieces are crowded together for finalfusion depends on a number of factors including: the mass of theworkholder; the velocity of the workholder at the moment of impactbetween the two workpieces; the effect of the spring in decelerating theworkholder; and the resistance to deformation of the heated portions ofthe two workpieces. Obviously adjusting the crowding action to the needsof different workpieces is complicated.

is highly advantageous.

7. Since the moving workpiece is part of the electromagnetically drivenworkholder, changing over from one size of workpiece to anotherintroduces a variable in that it changes the mass that iselectromagnetically accelerated.

8. It has been found that an arc welding device of the character musthave a certain relatively wide range of flexibility. At one extreme theare employed to join two pieces of copper must be intense for generatingheat at a relatively high rate but must be of short duration because ofthe high conductivity of copper. At the other extreme, the welding of analloy containing zinc is made possible for the first time by employing alow intensity arc of prolonged duration. Thus for welding copper the arcmay have a duration of one-third of a millisecond while an arc for azinc alloy may have a duration of 8 milliseconds. in addition the rateat which the gap is closed between two workpieces must bevariable'because the different physical properties of different moltenmetals affects their I behavior as they are forced together. This priorart apparatus is inherently incapable of flexibility in these importantrespects.

The present invention is not only directed to the elimination of thesedisadvantages but also is directed provements in the circuitry forproducing the SUMMARY OF THE INVENTION arc.

matic operating cycle, a rotary cam means formed with twocircumferentially spaced lobes is engageable with a continuouslyrotating structure of relatively high mass through speedreducing gearingby means of a clutch which rotates the cam for one full revolution forone complete cycle of operation and then the cam is stopped at itsstarting position by a suitable brake. A first workpiece is frictionallyslidingly mounted in a stationary workholder and the second workpiece isfirmly mounted in a movable workholder that is reciprocated twice by afollower cooperating with the two lobes of the cam means. The firstslidable workpiece is located in a random manner on the first workholderat a position advanced somewhat towards the second workpiece and whenthe second workpiece is reciprocated by the first cam lobe, the secondworkpiece encounters the first workpiece and retracts the firstworkpiece accurately to a starting position for carrying out the workcycle. When the second workholder retracts, the distance between the twoworkpieces is precisely the magnitude of its retraction regardless ofthe initial position of the first workpiece in the first workholder andregardless of the initial position of the second workpiece in the secondmovable workholder. Thus the first reciprocation results in accuratepredetermined starting gap between the two workpieces.

After a short pause controlled by a lower dwell on the rotary cam means,the movable workholder is reciprocated again to close the gap betweenthe two workpieces and at a precisely predetermined point in therotation of the cam means an arc is triggered between the two spacedworkpieces to melt the metal of the confronting surfaces of the twoworkpieces and the second workholder continues to advance the secondworkpiece after the two workpieces abut each other, the additionaladvance crowding the workpieces together for complete fusion of theheated portions of the workpieces. The force with which the fusingworkpieces are crowded together may be limited to any desired magnitudeby simply varying the friction with which the workpiece is slidinglyretained in the stationary workholder.

At the start of the operating cycle, the two workpieces are simplyplaced at suitable positions on the two workholders and as soon as theoperating cycle is started the two workholders automatically grip thetwo workpieces. At the end of the operating cycle the two workholdersautomatically release the welded product and then the welded product isautomatically ejected.

After the first reciprocation of the movable workholder, a voltage isplaced across the two workpieces and subsequently to important imthe arcis triggered in the response to arrival of the second workpiece at aprecisely predetermined point in its second movement towards the firstworkpiece. To create the desired voltage across the two workpieces, thecam means operates a relay for connecting capacitor means to a voltagesource and alternately to connect the capacitor means to the twoworkpieces; means controlled by the cam means keeps the initiallyengaged clutch engaged until a suitable point near the end of theoperating cycle; further means controlled by the cam means operatessolenoids for gripping the two workpieces; further means operated by thecam means controls a third solenoid for ejecting the finished product;and still further all important means controlled by the cam meanstriggers the are at an exactly predetermined point in the approach ofthe movable workpiece to the stationary workpiece.

The manner in which the described cycle mechanism avoids the previouslymentioned disadvantages of the prior art mechanism is explained asfollows:

I. With a driving structure of relatively large mass rotating at aconstant velocity for a normal steady state condition, frictionalresistance to movement of the driving mass is eliminated and with themass of the driving structure far exceeding the mass of the movableworkholder, frictional resistance to movement of the workholder may beneglected.

2. A spring is provided to hold the workholder follower against the cammeans and to return the movable workholder after each advance but thespring force is more than adequate to maintain constant contact betweenthe workholder follower and the cam means with the result that thespring itself does not affect the operating cycle and especially sobecause of the mass of the driving structure.

. Since the cam means is fully accelerated by the high momentum of thedrawing mass prior to actuation of the movable workholder thedisplacement of the workholder follower by the leading slope of thesecond cam lobe is at an accurately predetermined rate for accuratecontrol of the rate at which the gap between the two workpieces isclosed after the arc is triggered.

4. Since no time interval is required in the operating cycle foracceleration of the constantly rotating mass, acceleration is removed asa factor and the operating cycle may be correspondingly shortened.

5. Since the arc is triggered in response to the arrival of theworkholder follower at a precisely predetermined point in the rotationof the cam means, the timing of the triggering of the arc is preciselypredetermined in advance of mutual abutment of the two heatedworkpieces. Thus the correlation of the ignition of the arcwith theclosing of the gap may be accurately maintained over a long productionrun.

6. Since the first reciprocation of the movable workholder accuratelyestablishes a predetermined gap between the two workpieces and since theadvance of the second workpiece on the second reciprocation of themovable workholder exceeds the first advance by a predeterminedincrement, the extent to which the two workpieces are crowded togetherin the final fusing step is accurately predetermined and is constantover a large production run. With the crowding action accomplished bythe cooperation of the follower and the cam means, the crowding actionis not determined directly by the magnitude of the moving mass nor is itaffected by any spring means nor is it necessarily limited by theresistance to deformation of particular workpieces.

7. Changing over from the processing of workpieces of a Y given mass tothe processing of workpieces of a different mass only slightly affectsthe rate at which the two workpieces are brought into mutual contactbecause the ratio between the high momentum of the driving mass and therelatively small mass of the movable workpiece is exceedingly high, say2,200: 1. This fact may be appreciated when it is considered that in thepreviously described cycle of operation disclosed in the Phillips U.S.Pat. No. 3,254,193 the ratio between the approximately one ounce weightof the workholder and the one-tenth gram weight of a typical smallworkpiece mounted on the core is approximately 260:] whereas in thepresent invention the ratio between the weight of the driving structureand the weight of the same workpiece is approximately 10,000: I. Thevelocity of the driving structure results in a momentum of approximately48 pounds which is approximately 200,000 times the mass of theworkpiece. It may be readily appreciated that with this overpoweringratio, the driving mass acts like a stabilizing flywheel to insure thatall of the operating cycles are precisely identical. Changing over to adifferent workpiece of a different weight may vary the operating cyclebut only to slight degree and in any event the new cycle pattern isaccurately reproduced on each cycle.

Since the momentum of the driving structure on which the operating cycleis based varies with its velocity, it is desirable to move the drivingmass at high velocity. On the other hand, high velocity of the drivingmass may result in moving the two workpieces together at an undesirablyhigh velocity. A feature of the invention in this regard is theprovision of suitable speed reducing means for operatively connectingthe movable workpiece with the driving mass. In the initial practice ofthe invention the motor for driving the cam means rotates at a desirablehigh velocity for the sake of high momentum but reduction gearingreduces the angular velocity of the cam means to onesixth of the angularvelocity of the motor rotor and, if desired, further reduction in thevelocity imparted to the movable workpiece may be provided by formingthe lobes of the cam means with gradual leading slopes.

As will be apparent, the new circuitry has unique advantages includingadjustability of the intensity and duration of the arc, suchadjustability being provided by adjustability in the capacity of thecapacitor means that is charged to provide the energy of the are, aswell as adjustability in the voltage of the applied charge andadjustability in the impedance of the arc-sustaining circuit. In thepreferred practice of the invention a choke coil may be placed in thearc-sustaining circuit whenever desired and different taps on the chokecoil may be used for different degrees of impedance by the choke coil.

The flexibility of the operating cycle may be appreciated when it isconsidered that the magnitude of energy expended in the arc may bevaried at will and the duration of the arc may be varied independentlyof the total are energy. A further feature of the invention in thisregard is that the timing of the triggering of the are relative to themoment of contact of the two workpieces is also readily adjustable bythe simple expedient of changing the position of a contact thatcooperates with the cam meansto trigger the arc. In the preferredpractice of the invention the triggering contact is moved by a manuallyoperable knob that shifts the contact by screw action and a pointeroperated by the knob traverses a scale that is calibrated inmicroseconds of duration of the arc.

With exact control over the three factorsof are energy, are duration andthe timing of the triggering of the arc relative to the closing of thegap between the two workpieces, the welding function may be readilyadjusted to meet the specific requirements of any particular pair' ofworkpieces. Thus the energy of the arc may be adjusted as required formelting dif ferent metals and for melting different quantities of thedifferent metals and the duration of the arc may be shortened tominimize the melted zones of the workpieces or maybe extended whendesirable to vaporize oxides and impurities prior to the moment ofmutual abutment of the workpieces.

The various features and advantages of the invention may be understoodfrom the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to beregarded as merely illustrative:

FIG. 1 shows womewhat schematically and partially in a perspective view,the mechanical part of the welding apparatus in accordance with thepresent invention;

FIG. 2 illustrates a cross-sectional view through the guide system forone of the workpiece holders used in the equipment shown in FIG. 1.;

FIG. 3 is a development of the cam used for controlling the motion ofone of the workpiece holders shown in FIG. 1;

FIG. 4 illustrates somewhat schematically a circuit diagram, partiallyas a block diagram, of the control of the welding current and arcignition control circuit in accordance with a first embodiment of thepresent invention;

FIG. 5 illustrates an alternative embodiment of this invention partiallyas block diagram and partially as circuit diagram;

FIG. 6 is a diagram showing developments of five cams on a common camshaft that may be employed to carry out the operating cycle;

FIG. 7 is a schematic view showing different stages in the tworeciprocations of the movable workholders;

FIG. 8 is a simplified elevationalview of the two workholders;

FIG. 9 is a side elevational view of the stationary workholder;

FIG. 10 is a fragmentary view partly in side elevation and partly insection showing the mechanism for varying the timing of the triggeringof the arc relative to the closing of the gap between the twoworkpieces;

FIG. 11 is an elevational view as seen along the line 11 11 of FIG. 10showing a scale that is associated with the mechanism in FIG. 10, thescale being calibrated in microseconds of duration of the arc; and

FIG. 12 is a wiring diagram modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Proceeding now to the detaileddescription of the drawings, FIG. 1 thereof illustrates a weldingapparatus in accordance with the present invention. The illustration issomewhat schematically but partially in a perspective view. Of specificinterest is the welding of small elements. For example, in FIG. 1, thenumerals l0 and 11 denote two workpieces to be welded together. Element10 is a semiconductor device such as a transistor, an integratedcircuit, etc., encapsuled in a metallic shell. The other workpiece is aconnecting wire 11 to be connected to element 10. One can see that thewelding process is a most critical one because an excessive heatdevelopment will destroy the semiconductor device in the interior of thecontainer, whereas too little thermal energy developed will produce anunsatisfactory weld. Since effective thermal energy is determined by thebalance of heat inflow and outflow at any instant, the duration of theperiod during which a particular amount of electrical energy is suppliedand converted into thermal energy is most critical. Therefore, thewelding, i.e., thermal, energy and the development of that energy, i.e.,the duration of the weld, all have to be determined rather accurately inorder to produce a satisfactory weld which does not destroy the product.

The welding device proper includes a workholder 20 having an opening orpocket 21 into which a workpiece can be inserted. The pocket 21 has aconfiguration adapted to receive and position a particular workpiece inthe form of an encapsulated transistor. Of course, a different type ofholder may be used for a workpiece of different configuration. It isimportant that the particular holder positions the one workpiece in amanner to expose a surface portion thereof to which the other workpieceis to be welded.

Reference numeral 22 denotes another workholder which is stationary.Holder 22 has a groove 23 over which is placed a clamp 24 forfrictionally holding a workpiece in the form of a wire 11 in the groove.The clamping action is strong enough to grip the workpiece effectivelyto carry out the fusing or forging of the two workpieces but is lightenough to permit initial slippage for the purpose of accuratelydetermining the gap between the two workpieces.

The workholders are at least partly made of metal so that electricvoltage potentials can be applied to the workpieces thereon. It followsthat workholders 22 and 24 must be electrically insulated from eachother. A wire 25 connects the workholder 22 to a welder current controlcircuit 100, to be described more fully below, and a flexible electricalconnection 26 leads from the welder control circuit to the workholder20.

The workholder 20 is movably disposed on a vertically movable rod 30.The rod 30 is prevented from tilting by a guiding arrangement 31. Aportion of the guiding arrangement is shown in a cross-sectional view inFIG. 2. The rod 30 may have a portion hexagonal cross-section that isguided by two sets of three rollers each; one of the sets is shown inFIG. 2. There are two rollers 32 and 33 which have a fixed axis ofrotation and engage two different sides of the rod 30. The axes of therollers 32 and 33 are at an angle of l20. The shaft of the third roller34 is under the influence of springs 35 urging the shaft towards the rod30. The springs thus provide for positive engagement of all threerollers with the rod. As stated above, there is a second set of rollersfor additionally guiding the rod 30. If the second set of guide rollersis accurately mounted in vertical alignment with the one illustrated,rod 30 is accurately guided for vertical longitudinal motion.

The lower end of the rod 30 terminates in a cam follower 36. A spring 37is anchored at one end to a stationary part of the device and its otherend is anchored to a pin 38 which, in turn, projects from rod 30. Thespring is biased to urge pin 38 in down direction to thereby urge thefollower 36 of the rod 30 into engagement with a cam 40. The cam 40 iscapable of pushing bar 30 in up direction, while spring 37 retracts bar30 when the moving contour of cam 40 so permits.

The cam 40, and particularly the periphery 41 thereof, servesadditionally to control a switch 51 which has an appropriate followerarm and which is connected electrically to the welder control circuit100 in a manner to be described more fully below. A projection 48 on thecam 40 serves to control a second switch 52 which likewise pertains tothe welder control circuit 100 and to which will be made reference morefully below. On this particular embodiment of the invention the switch51 responds to the same cam lobes that control the follower 36 of theworkholder rod 30.

Cam 40 is provided with a spur gear 42 meshing a pinion 43 on a shaft 44which is operatively connected to a brake-clutch assembly, generallydesignated 45, comprising a brake 45a and a clutch 45b. The rotary inputof the clutch 45b is derived from a shaft 46 driven by a synchronousmotor 47. The synchronous motor 47 is continuously connected, at leastduring extensive welding operations, to an a-c source of standardfrequency. Motor 47 thus imparts to the shaft 46 a preciselypredetermined rate of rotation. The brake-clutch assembly 45 iscontrolled by a common switch 50, the brake 46a disengaging and theclutch 46b engaging in response to closing of the switch and vice versa.As will become apparent more fully below, switch 50 initiates a cycle ofoperation that is carried out by one revolution of cam 40.

A welding operation, in summary, is carried out in the following manner.While the motor 47 runs continuously, the encapsuled transistor element10 is placed in the cavity or pocket 21 of the workholder 20 and thewire 11 is placed in the groove 23. The position of capsule 10 isdefined by the contour of pocket 21, but wire 11 is variablepositionable in groove 23 of holder 22. Subsequently switch 50 is closedso that clutch 45 energized. The energized clutch couples cam 40 tomotor 47. The cam 40 then performs one revolution. After a completerevolution either the switch 50 is opened manually or through aconventional control circuit which may include an additional cam, or cam40 itself may be used to interrupt the clutch circuit. This type ofinterrupt control is well known and of course, the control may becarried out manually if desired.

During the one revolution the cam 40 controls the entire weldingoperation. As will be described more fully below, the cam causes the arm30 first to preposition the two elements 10 and 11 to define the size ofthe gap across which an arc is to be struck. Thereafter the switches 51and 52 are closed sequentially to energize the welder control circuit100 in that a low voltage is applied first to the wires 25 and 26 and tothe workpieces and subsequently a high voltage is developed to strike anarc. In precise synchronism with are ignition the cam 40 moves the twoworkpieces 10 and 11 again towards each other, brings them into contact,maintains that contact until cooled and retracts them together.

Proceeding now to the description of FIG. 3 there is shown thedevelopment of the contour of periphery 41 of cam 40. The base line r inFIG. 1 corresponds to the smallest radius of the cam 40 with referenceto its axis of rotation and it defines, therefore, the lowest portion ofthe cam (except for a modification to be discussed separately). The camprovides for reciprocating motion of follower 36, for example, in thevertical direction. Hence, cam radius r defines the lowest position offollower 36 (and, of course, of workpiece holder 20). The follower is atthis lowest position when the system is at rest, i.e., in between welds.The contour of the leftmost side of the diagram shown in FIG. 3 has thisradius r and defines the position of follower 36 at the beginning of theoperating cycle. It is convenient to describe the various portions ofthe cam contour with reference to the sequential control effects exertedby them upon workholder 20 as these portions progressively control theposition of the follower 36 during rotation of the cam 40.

In FIG. 3 the particular cam portion controlling the idle position offollower 36 which actually is an indentation in the cam, is furtheridentified by t which means that we assume that at the starting time tthe switch 50 may be closed to initiate rotation of the cam. The portion41 1 of cam 40 that subsequently controls follower 36 is characterizedby an increasing radius thus causing the follower 36 along withworkholder 20 to move in upward direction. The cam portion 411terminates in the lobe 412 which actually is a portion of constantradius r of the cam disk 40, the radius r being larger than the radiusr.,. Therefore, when the follower 36 reaches the portion 412 it has beenmoved in upward direction by the difference r r It was stated above theworkpieces and 11 were placed into the respective workholders and 22prior to the time t when the workpiece holder 20 is at its lowermostposition. Also, it was stated that wire 11 does not have to bepositioned very accurately into groove 23, but the lower tip of wire 11must be initially spaced from the other workpiece 10 at a distance whichis smaller than r r In fact the two workpieces may be initiallypositioned in contact with each other provided that workpiece 11 is nothigher than r r above workpiece 10.

It follows, therefore, that during the time the cam portion 411 ofincreasing radius advances the position of follower 36, workpiece 10will meet the wire 11 but thereafter workpiece 10 in workholder 20continues to move upwards. As was stated above, the clamping force forthe wire 11 is slight and as the upward stroke of the workholder 20continues, the workpiece 10 pushes the wire 11 also in up direction.

At time 1 the upward motion of follower 36 stops because the cam portion412 succeeding portion 411 is a dwell of the radius r Thus, after time 1workholder 20 and workpieces 10 and 11 are temporarily at rest. It isapparent that it is immaterial which workpiece is shifted relative toits holder and which one stays fixed, or whether both of them shift. Theinitial position of the two workpieces is completed by time t,.Presently the workholder 20, acting through the workpiece 10, has nowactually placed the wire 1 1 in a particular position relative to itsholder 22. If, subsequently, the workholders are moved apart by aparticular distance, the workpieces will be automatically spaced apartby that distance.

The dwell or plateau 412 of constant radius r, does not have to be toolong but some length is required to provide for some settling so thatthe position of the wire 11 is positively defined. It is emphasized thatup to that point no current flows through the welding system. At a timet a gap between the two workpieces is initiated because a portion 413 ofcam 40 reaches the follower 36 which portion 413 is defined by adecreasing cam radius. Therefore, the spring 37 causes retraction of thefeeler arm 36, and the workholder 20, retracts accordingly. Thusworkpiece 10 separates from the workpiece 11 at the time t, andcontinues to retract therefrom. At the time the cam portion 413 levelsoff to a lower dwell 414 of constant radius r,, and while follower 36slides over this lower dwell, workholder 20 is maintained at aparticular, retracted position. The workholders have thus been retractedover a distance r r as defined by the difference between the cam radii rr.,. The difference r r defines also the present distance between thetwo workpieces, this distance being the maximum air gap distance overwhich an arc may be ignited.

During the period in which the follower 36 maintains workholder 20inretracted position, switch 51 is closed which may be at any time after tfor example at time 1 In response thereto the welder control circuitcauses a low voltage to be applied to the wires 25, 26. As stated, thisvoltage is insufficient to strike an arc across the gap between the twoworkpieces 10 and 11, which gap is of the dimension r r Switch 51 ispositioned in advance of follower 36 with reference to the direction ofrotation of cam 40, and is operated by the lobe 416 of largest radius.The function of that lobe with reference to follower 36 will bedescribed below.

The switch 52 may be closed to trigger the are at any selected time andafter time and before the follower 36 climbs the cam slope 415 at time tat the level of the initial upper dwell 412 that is indicated by thebroken line 412a and thereby brings the heated workpieces together. Theare is extinguished when the follower 36 brings the two workpiecestogether, but because the cam slope 415 continues to rise above thelevel 412a, the two workpieces are forcibly crowded together to fusetheir molten end portions together. The second upper dwell 416 ofconstant cam radius r, is reached at time t,. The welding arc currentflows during the period between the times t and The friction with whichthe wire 1 1 is held in holder 22 is sufficient to resist the initialcrowding force and only after the softened portions of wire 11 andelement 10 have been driven into each other does the wire 11 move bodilyin response to the crowding force.

In the time interval between t, and t the upper dwell 416 of constantradius r keeps the follower 36 stationary.

It will be recalled that switch 51 is angularly displaced from follower36 so that cam lobe 416 operates the switch earlier in a welding cyclethan the arrival of the follower 36 at this cam lobe. The switch 51 maybe closed by came lobe 416 at any time between time and time At time aportion 417 of declining radius of the cam reaches the follower 36 andspring 37 causes the workholder 20 to retract according to the slope ofcam portion 417. During the downward retraction of workpiece 10, wire 11is welded thereto and slips out from under the clamp 24.

At about the time t,, the operating cycle is completed and switch 50opens to stop cam 40. The two pieces which have been welded together maythen be removed from the workholder 20 in preparation for a newoperating cycle.

It shall now be described how the switches 51 and 52 control the entirewelding process, to the extent that they are themselves controlled bycam 40. A representative example of the control circuit 100 is shown inFIG. 4.

Reference numeral 60 generally denotes an electric power supply unit forthe welding control circuit in accordance with the present invention.The power supply includes a transformer 61 having a primary 62 which isconnected to the same external power supply source, for example, themains, as are motor 47 and brake-clutch assembly 45. This transformer 61has a core on which there are two secondary windings which are not shownin detail.

Reference numeral 63 denotes a low voltage d-c power supply for thewelder circuit which is also not shown in detail but it includes on thesecondary windings of transformer 61 for voltage step-down. The lowvoltage d-c source 63 includes further a conventional rectifier tosupply a particular d-c voltage potential to an output line 64, theoutput being variable in a range of 40 to 100 volts. The network 63 mayinclude additionally a voltage regulator such as, for example, atransistor serving also as rectifier and having in its control circuitsuita ble, adjustable impedance means for adjusting the d-c voltage forline 64. Alternatively or additionally the secondary winding oftransformer 61 feeding the a-c voltage to the rectifier in unit 62 maybe adjustable. All of these elements are conventional and do not requireelaboration, since they are shown in the above mentioned US. Pat. Nos.3,254,193; 3,254,194; and 3,254,195. A second d-c output line 64bprovides d-c voltage at a different level.

Reference numeral 65 denotes a high voltage d-c power supply unit whichdoes not require regulation as the voltage constancy and the levelaccuracy of the mains suffices here. The unit 65 includes anothersecondary winding of the transformer 61, preferably having a highernumber of turns than the primary 62 to provide for voltage step-up. Theoutput line 66 of unit 65 receives a high d-c voltage, for example, of800 volts positive relative to ground, whereas a second output line 67of unit 65 receives a negative d-c voltage potential of 800 voltsnegative relative to ground, so that the potential difference betweenthe lines 66 and 67 is 1,600 volts. These voltages will be used to feedan arc ignition circuit.

The d-c voltage of line 64 is passed to an adjustable capacitor bank 70.The capacitor bank includes a plurality of capacitors individuallyconnectible through resistors between the line 64 and ground so that aparticular amount of electric energy can be stored. The total chargedepends, of course, on number and size of the capacitors placed intocircuit to be charged and on the voltage applied through line 64 forcharging. Both total effective capacitance and voltage determine theamount of energy available for discharge. The electrical energyaccumulated in capacitor bank 70 can be discharged through the line 71,and the voltage in line 71 will be essentially the same as in line 64.

The lines 64 and 71 are now in addition governed by the contacts 76, 77of a relay 75. The energizing coil of the relay 75 is under control ofthe switch 51, mentioned above. Switch 51 when closed connects relaycoil 75, between ground and line 64b which is constant, non-adjustablelow voltage d-c output of the unit 63. As long as relay 75 is notenergized contact 76 is closed and contact 77 is open. This is thenormal state as switch 51 is, in fact, normally open (up to time as wasexplained above). Therefore, the relay 75 is normally unenergized so asto permit the capacitor bank 70 to be charged through the normallyclosed contact 76. On the other hand, contact 77 is normally open toprevent any discharge of the capacitor bank 70, accidentally orotherwise, during the charging process. Moreover, contact 77 governs allthose circuit portions with which personnel may come into contact priorto the actual welding operation and the open contact 77 permits theprepositioning of workpieces as explained above.

When relay 75 energizes, contact 76 opens and contact 77 closes tothereby provide a connection from the capacitor bank to a series circuitnetwork which includes directly a feedthrough capacitor 78, secondarywinding 82 of a saturable core type transformer 81, the line 25mentioned above and one of the workpieces which, in this case, is thewire 11. As long as no arc exists across the gap between workpieces and11, or as long as the workpieces 10 and 11 do not contact each other,the high impedance of the unionized gap holds that series circuit openeven when contact 77 is closed.

The wire 26 connects the other workpiece 10 to ground as was alreadymentioned above. Therefore, with a gap between the two workpieces l0 and11, the capacitor bank 70 can discharge when the contact 77 closes,provided there is an arc between the two workpieces. As mentioned above,the switch 51 closes at time As shown in FIG. 1, the follower arm of theswitch 51 is positioned ahead of the follower 36 with respect to thedirection of the rotation of cam 40. Therefore, the lobe 416 which isthe one with the largest control radius r will enter the range of thefollower am of switch 51 ahead of the follower 36. Particularly switch51 closes when follower 36 has completed the positioning of a workpiece10 at the desired gap distance from workpiece 11. Contact 77 is closedand the capacitor bank voltage becomes effective across the gap betweenthe workpieces l0 and 11 only after the prepositioning of the workpieceshas been completed, and when they are separated from each other by thecam lobe difference r, r It is essential that the voltage then appliedacross the gap between the two workpieces be insufficient to strike anarc. Therefore, for igniting an arc additional provision must be made aswill be described next.

The control circuit for arc ignition is divided into an arc ignitingcircuit, generally designated 80, and a trigger circuit, generallydesignated 90. The are igniting circuit 80 includes a multi turnsecondary winding 82 of saturable core type transformer 81 that has aprimary winding 83 of but a few turns. For example, the winding 82 mayhave 29 turns and the winding 83 may have 2% turns so that the voltagestep-up ratio is about 1:12 for developing an extremely high voltageacross the secondary winding 82.

One end of the primary 83 is connected through a capacitor 84 to anelongated, high refractory type electrode 85a of an electrode systemthat is generally designated 85. Representa tively, electrode 85a may bea cylindrical rod of W2 inch length and one-fourth inch diameter. Theother side of the winding 83 is connected through a second capacitor 87to an electrode 85b which is similar to electrode 85a and which is alsoin the electrode system 85. Capacitor 87 is overbridged by a resistor 89of, for example, 15 KO. Electrodes 85a and 85b are placed in parallel(physically) and at a distance of about one-half inch from each other.They are respectively connected with their other ends to the highvoltage d-c power supply lines 66 and 67 using individual high ohmicresistors 88a and 88b, respectively for the connection. Each of theresistors 88a and 88b may have a resistivity of the order of 100 K O. Athird electrode 850, in the electrode system 85 is of similarconfiguration as the other two electrodes and is interposed between themand in parallel spacial relationship thereto.

Electrode 850 does not extend all the way into the gap betweenelectrodes 85a and 85b. Thus, there are now defined three air gaps. Thefirst one, 86a, is between electrodes 85a and 85b beyond electrode 85c.The second gap 86b is between electrodes 85b and 850, and the third gap86c is between electrodes 85c and 85a.

The capacitor 84 is connected directly to the high voltage power supplysource 65 through resistors 88a, 88b and 89. Thus, capacitor 84 isnormally charged to 1600 volts. The charge time is short in relation tosequential welding cycles as defined by revolutions of cam disk 40, sothat the capacitor 84 is always charged when needed. The gap 86a is sowide so that the 1600 volts thereacross are not sufficient to strike anarc. The electrode 850 is normally grounded so that across each of thegaps 86b and 86c there are 800 volts and these gaps are likewise toolarge for ignition of an arc. Thus, normally there is no arc across anyof the gaps in the electrode system 85, and there is no voltage acrossthe windings 82 and 83. Also, any charge current for capacitor 84 isquite low and the charge is completed before contact 77 closes within awelding cycle.

The trigger circuit 90 for the arc igniting circuit 80, includes atransformer 91 which is of the flyback type and has a saturable core, ahigh voltage, secondary winding 92 and a low voltage primary winding 93of fewer turns than the secondary winding. The secondary winding 92 isconnected between electrode 850 and ground, so that electrode 85c is atground potential as long as no voltage is induced in winding 92. Acapacitor 94 is connected to ground and to one of the low d-c voltagesupply lines, for example, previously mentioned line 64b and through ahigh ohmic resistor 96. The capacitor 94 serves as a temporary powersupply for the trigger circuit.

One end of the primary winding 93 is connected to the junction betweencapacitor 94 and resistor 96, the other endof the primary winding 93 isconnected to one main electrode (here the cathode) of a siliconcontrolled rectifier 95 having its anode electrode grounded. The controlelectrode of rectifier 95 is connected through an RC circuit 99 to oneside of the previously mentioned switch 52, which when closed, connectsthe control electrode of the silicon rectifier 95 to the same source forthe anode potential thereof which is ground.

To explain the function of the trigger and arc ignition circuits,reference is made first to FIG. 1 and to the cam configuration shown inFIG. 3. It will be recalled that at the time the switch 52 was caused toclose and that thereafter the gap between the two workpieces closes.

Switch 52 closes the control circuit for the silicon controlledrectifier or semiconductor type thyratron 95. The contact of switch 52can be expected to rebound, but the initial closing fires the rectifier95. This requires less than a microsecond, so that any rebounding ofcontact 52 has no effect on the continued state of conduction ofsemiconductor device 95.

As silicon controlled rectifier 95 conducts, it connects the chargedcapacitor 94 across the primary winding 93. The capacitor dischargesvery rapidly and a high voltage surge is produced across the winding 92.The peak value may be 800 volts or thereabouts. The polarity of thevoltage is immaterial but in this instance the voltage across thesecondary 92 is positive relative to ground. As stated, the electrode850 has normally ground potential but its potential is now raised byseveral hundred volts, for example, up to 800 volts. The gap 86b betweenthe electrodes 85b and 85c is sufficient to prevent an arc at thevoltage of 800 volts which prevails across the gap as long as theelectrode 850 is at ground potential. With the potential of electrode85c now raised up to about 800 volts positive, the voltage across thegap 86b increases to about 1600 volts. Actually, before that value isreached the gap breaks down and an arc is developed in between the twoelectrodes 85b and 85c, immediately lowering the potential of electrode85c to approximately the -800 volt level of electrode 85b so that thefull 1600 volts becomes immediately effective across the gap 86c betweenthe electrodes 85a and 850 which breaks down likewise.

The delay in between the sequential or cascaded firing of the gaps 86band 860 covers a period which is in the microsecond range and below, soare the delay between firing" of semi-conductor device 95 and thedevelopment of the ignition voltage across secondary 92, so that anelectric connection is established between the electrodes 85a and 85b afew microseconds or less after the switch 52 has closed. The arcs in theelectrode system are sustainedby discharge of capacitor 84. Primarywinding 83 and capacitors 84 and 87 form a high Q resonant circuit. Thehigh transformer ratio of transformer 81 causes an oscillatory voltagepulse to develop across the winding 82 with peak values in theneighborhood of to 20,000 volts, depending on the step-up ratio oftransformer 81.

It will be recalled that switch 51 cause, through relay 75, contact 77to close at time 1 i.e., prior to the time when switch 52 closes. Thus,as the high voltage peak is developed across winding 82, a voltageacross the workpieces 10 and 11 has already been established. Thisvoltage is the capacitor bank voltage in line 71, which, by itself, isinsufficient to strike an arc across the gap defined between theworkpieces, up to time At the time the voltage developed across thesecondary winding 82 raises the potential of the workpiece 11 to such anextent that breakthrough occurs with certainty instantly and onlymicroseconds or less after the initial closing of the switch 52. Thatdelay is a fixed one and does not depend upon any particular conditionssuch as the shape, size, weight, of the workpieces. As it is a fixeddelay time, with variations being of the order of electron statistics,one can regard it as a predetermined system constant. Variations inaccordance with the electron statistics can be disregarded for thepurpose of this device.

As the arc is ignited across workpieces 10 and 11, the gap ionizes. Thevoltage of capacitor bank 70 suffices to sustain and continue the arc.The voltage level of bank 70 and the total amount of energy storedtherein are adjusted that at the time 2 the energy stored has beensubstantially discharged and thus converted into thermal energy by thearc. The thermal energy has thus heated and softened the workpiece endsfor the particular period of time, 1 At the time I the work pieces 10and 1 1 make mutual contact and the upward motion of the workpiece l0continues to crowd the two workpieces together until the weld iscompleted.

Referring again to the arc ignition and continuation, the gaps 86b and86c break down sequentially, thereby effectively interconnectingelectrodes 85a and 85b. These two arcs initiate in the left handportions of either electrodes 85a and 85b, which is somewhat remote fromcapacitor 84, i.e., from the source which actually feeds the two arcs.These two arcs now migrate to the right to reduce the effectiveresistance in I the discharge circuit for the capacitor 84, and soon thearcs merge to cross directly the gap between electrodes a and 85b.Electrode 85c becomes effectively disconnected from electrodes 85a and85b so that the trigger circuit is removed as a load from the dischargecharge circuit of capacitor 84. The removal improves the Q of the tankcircuit.

As soon as an arc is ignited across workpieces 10 and 11 the effectiveimpedance across winding 82 drops to a very low value, basically that ofthe ionized gap between the workpieces, so that capacitor 84 dischargesalso into the main gap. The effective impedance of this additionaldischarge circuit is reduced in accordance with the ratio of the primaryand secondary windings of transformer 81. The energy stored in capacitor84 will rather quickly be exhausted and the arc in the electrode system85 will extinguish. The resulting open circuit state for the tankcircuit prevents any of the energy stored in capacitor bank 70 fromflowing into a parasitic circuit such as the now active ignitioncircuit. This, however, is not too important an aspect, as the core oftransformer 81 will saturate when the capacitor bank 70 discharges, witheffectively discouples the ignition circuit from the main discharge pathto the two workpieces.

A complete operating cycle can be briefly described in summary asfollows. Normally the cam 40 is at rest and contacts 51 and 52 are open.Thus, relay 75 is deenergized, contact 76 is closed; the capacitor bank70 is being charged but contact 77 is open so that no potentialdifference is set up between the two workpieces. The capacitor 84 ischarged to 1600 volts, but no arc exists in the electrode system 85.Capacitor 94 is charged to a low voltage. Semiconductor 95 isnon-conductive.

After the workpieces l0 and 11 have been positioned properly but notnecessarily very accurately, (for example, manually), switch 50 isclosed and cam 40 begins to rotate. As the workholder 20 moves upwardworkpiece 10 contacts workpiece 11 and pushes it in upward direction. Ascontact 77 is open, no current flows between the two workpieces. Theupward motion is stopped at a particular point and subsequently theworkholder 20 is retracted, leaving the workpiece 11 in a particularposition. The retraction of workpiece 10 on workholder 20 covers aparticular distance, which is the gap distance between the workpieces l0and 11.

After this prepositioning of the workpieces, switch 51 closes toenergize relay 75 to disconnect the supply 63 circuit from the capacitorbank 70 and to connect the capacitor bank to the two workpieces.

Switch 51 should close sufficiently ahead of the ignition of an arc tomake sure that contact 77 has ceased to rebound by the time switch 52closes. On the other hand, switch 51 should close as late as possible tokeep workpieces l0 and 11 at the same potential as long as possible as aprotective measure for personnel.

Switch 52 closes at the time t and the first closing impact of themovable contact on the stationary contact of the switch fires thesilicon controlled rectifier 95 to produce a high voltage pulse acrosssecondary winding 92 which, in turn, fires in sequence the two gaps 86band 860 in the electrode system 85 to thereby close the tank circuitwhich includes the two capacitors 84 and 87 and the winding 93. Theresulting oscillatory discharge of capacitor 84 produces an extremelyhigh voltage pulse across the winding 82 and an arc is struck across thegap between workpieces and 11. The impedance of the now ionized air gapis reduced permitting the capacitor bank 70 to discharge into theworkpieces.

At time i substantially all energy of the capacitor bank 70 has beendischarged so that by the time of contact between the workpieces 10 and11 a particular amount of thermal energy has been developed to melt themetal of the tips of the two I workpieces. As the workpiece 10 iscrowded upward again the wire 11, fusion occurs and the wire 11 isretracted. The two joined pieces 10 and 11 are left in the highestposition. After sufficient cooling, cam 40 and spring 37 cooperate toretract the joined pieces 10 and 11. Subsequently cam 40 reaches'itsinitial position and stops. The welded pieces can now be removed fromthe workholder 20.

Several outstanding features of this welding apparatus should bementioned. For example, the gap or the particular location of the gap isnot predetermined upon initially placing the workpieces into theirrespective holders. The workpiece 10, therefore, may have any kind ofsurface configuration and no accurate positioning tool for placing theworkpieces into the respective holders is required, nor does manualplacement require any great accuracy. Instead, the particular spot ofthe workpiece to which subsequently the other workpiece is to be weldedis used as a pushing surface to place the workpiece 11 into a particularposition. Thus, the entire arrangement automatically accommodates itselfto the particular configuration of the workpieces to be welded together.The points or surface areas of the two workpieces which are to be weldedtogether, are precisely the ones which are initially used to positionthe workpiece 11. Consequently, as the workpiece 10 is retracted fromthatparticular position for a precise distance, the gap is definedtherewith. The initial positions of the two workpieces relative to thetwo workholders are not factors in the determination of the width of thegap.

To provide a desirable range of control over the duration of the arc, achoke coil 97 is placed in parallel with a switch 98 between thesecondary winding 82 and the workholder for the workpiece I1. Normallythe switch 98 is closed to shunt the choke coil but the switch may beopened when prolongation of the duration of the arc is required. Thechoke coil 97 has a plurality of taps 97a which may be connectedselectively to the winding 82 for selected degrees of extension of theduration of the arc.

In FIG. 5 there is shown another embodiment of the present invention.The workpieces 10 and 11 are mounted in a hand gun, shown onlyschematically. One workpiece, here the grounded element 10 is stationaryin the gun, while the other element 11 is mounted on a movable holder. Ahammer 101 is normally retracted at a position arrested by a releasablestop 102. A spring 103 urges the hammer towards the holder for element11 but is prevented by the stop 102.

The hammer 101 is electrically connected to one side of the primarywinding 93 of the transformer 91; the other side of the winding 93connects to ground through an RC circuit 104. Secondary 92 oftransformer 91 is connected between ground and the previously mentionedelectrode 85c (not shown) in the electrode system 85 as in FIG. 4. Thehigh voltage source 65' for this embodiment may have only one outputline 67. It should be noted, however, that the arc ignition circuit maybe the same as the one shown in FIG. 4, while the one presentlydescribed is applicable for the welder described above with reference toFIGS. 1 to 4.

The high voltage of source 65 is applied through a filter 104 and theprimary 83 to capacitor 84. The junction between filter 104 and primary83 leads to electrode 8511, while the other side of capacitor 84 isgounded and also connected to electrode 85a. The remainder of thecircuit is as was described with reference to FIG. 4.

For operation switch 51 is closed first so that relay 75 can function asheretofore described and this may be done at any time before the weldinggun is triggered. Thus, the potential of the capacitor bank is appliedto workpiece 11, but is insufficient to strike an arc. The stop 102 maybe released concurrently or later and spring 103 causes the hammer 101to strike towards the workpiece 11.

The hammer 101 serves as a switch for connecting electrically theworkpiece 11 to the primary winding 93 of the trigger circuittransformer 91. A small portion of the charge of capacitor 70 flows intothe RC circuit 104 and that current flows through primary 93. Thus, inthis case the electrodes 85 are fired in a similar manner except thatthe voltages are somewhat differently rated. The full 1,600 volts arenormally across gap 86b and must thus not suffice to create an arc.However, the ignition voltage does not have to be large in this case tobreak that gap down. On the other hand gap 860 must break down when 1600volts are applied between the electrodes 85a and 85c. Thus, theelectrode 850 must be somewhat closer to electrode 85a than to electrode851;.

As hammer 101 contacts workpiece 11 the potential of electrode 85c israised to a level so that gap 86b between electrodes 85c and 85b breaksdown thereby causing the voltage of electrode 85c immediately to rise toa level so that gap 86c between the electrodes 85a and 85b breaks downalso. The ionized auxiliary discharge device 85 connects the capacitor84 directly across primary winding 83 and the resulting tank circuitresonates. Thus, the main arc ignites across the gap between workpiecesl0 and 11 as aforedescribed. Turning now to a second function of thehammer 101, its motion is predetermined by the characteristics and biasof spring 103. Thus, hammer 101 pushes the workpiece 11 towards theworkpiece 10 at a controlled rate to complete the weld. This deviceworks satisfactorily in case the weight and size of the workpieces arerather constant; otherwise, weight variations of the particularworkpiece that is being moved may cause variation in the time betweenthe arc ignition and the contact making. No such variation occurs in thedevice shown and explained with reference to FIGS. 1 through 4.

FIG. 7 is a visual summary of the stages of relative movement betweenthe two workpieces 10 and 11 at the different times t 2,. In FIG. 7 itis assumed that occurs on the cam slope 415 just before t FIG. 7e showsthe relative positions of the two workpieces at and FIG. 7f shows an arcdesignated 300 that is established at that instant. FIG. 7 further showshow the two workpieces make mutual contact at t and are then crowdedtogether to make the finished weld that is accomplished at FIG. 7 makesclear that with the two workpieces 10 and 11 positioned .at random inthe corresponding workholders in such manner that the two workpiecesabut each other at t the starting gap that is provided in preparationfor the welding operation is determined solely by the retraction of themovable workholder from the position t so that the gap at t is anaccurately predetermined gap that will be formed automatically on eachoperating cycle. At t, the two workpieces are charged with a voltage asindicated and the art may be established at the gap dimension shown int, which is the starting gap because 1 and t, are spaced apart by a camdwell of constant radius; or the establishment of the arc may be delayeduntil the two workpieces are relatively close together as indicated atFIG. 7f.

Referring back to FIG. 3 it may be seen that the dwell 414 is ofsubstantial circumferential extent and the leading slope 415 of thesecond lobe is of substantial circumferential extent. It is apparenttherefore that there is a substantial range for adjustment of theduration of the arc. For example, the range of adjustment may be from300 microseconds to 300 milliseconds.

FIGS. 8 and 9 show how two workholders 20a and 22a corresponding to thepreviously mentioned workholders 20 and 22 may be adapted for a fullyautomatic cycle which includes automatic clamping of the two workpiecesl and 11. The workholder 20a is in the form of a rod, one end of whichconstitutes a cam follower 36a that corresponds to the previouslydescribed cam follower 36 and cooperates in the same manner with thepreviously described cam 40.

The workholder 20a has a noncircular shank portion 200 which isslidingly mounted in a pair of spaced guides 202 and 204 with a coilspring 205 under compression between the guide 205 and a collar 206 onthe workholder to bias the follower 36a effectively against the cam 40.The workholder 20a has a leading stem portion 208 which forms a seat toreceive the workpiece 10, the stem portion being removable to permit thesubstitution of a different stem portion to accommodate a workpiece ofdifferent shape or dimension. A pair of jaws 210 is mounted on pivots212 to releasably clamp the workpiece l0 and the two jaws havecorresponding operating arms which are connected by a pair of togglelinks 214 to a pivot 215 on a armature 216 of a clamping solenoid 218.The armature 216 is normally advanced with the two jaws 210 open asshown in FIG. 8 but energization of the solenoid 218 retracts thearmature to close the jaws 210 to tightly grip the workpiece.

The stationary workholder 22a is formed with a straight groove 220 toslidingly seat the wire or workpiece 11 and a jaw 222 is provided toclamp the workpiece in the groove. The jaw 22 is mounted on a pivot 224and has an operating arm 225 that is connected by a coil tension spring226 to the armature 228 of a clamping solenoid 230. Here again thearmature 228 is normally extended with the jaw 222 retracted andenergization of the solenoid 230 retracts the armature to close the jaw.The spring 226 has a relatively light spring force which is sufficientto cause the workpiece 11 to be retained in the required slidablemanner.

Preferably the workholder 20a is further suitably provided with anejection solenoid 232 having a normally retracted armature 234. When thesolenoid 232 is energized the armature 234 advances with a snap actionto eject the finished welded product at the end of the operating cycle.

FIG. 6 indicates diagrammatically how a cam assembly of five rotary camsmay be mounted on a common cam shaft (not shown) to carry out a fullyautomatic cycle which includes the steps of temporarily clamping the twoworkpieces and subsequently ejecting the finished welded product. Thefive cams comprises: the previously mentioned cam 40 which cooperateswith the follower 36a to control the movable workholder 20a in themanner heretofore described; a cam 240 having a circumferentiallyextensive upper dwell 241 to cooperate with a normally open switch 242for energizing the two clamping solenoids 218 and 230 throughout themajor portion of the operating cycle; a cam 244 having a lobe with anupper dwell 245 to operate an associated switch 51a which corresponds tothe previously mentioned switch 51 for placing a voltage across the twoworkpieces; a cam 246 carrying a contact 247 to cooperate with a contact248 to serve as an arc-triggering switch in the manner of the previouslymentioned switch 52; a cam 249 having a short lobe 250 to operate acooperative switch 251 for momentarily energizing the ejection solenoid232; and finally, a cam 252 having a short lobe 253 to open a normallyclosed switch 254 to terminate the rotation of the cam assembly.

As shown in FIG. the normally stationary contact 248 may be mounted onan arcuated rack 260 that is concentric to the cam shaft and isrotatably supported thereon by a pair of arms 262. Teeth 264 of thearcuate rack mesh with a worm 265 on an adjustment shaft 266 that ismanually operable by a knob 268. The knob 268 carries a pointer 270which, as indicated in FIG. 11, is movable along a graduated scale 272that is calibrated in terms of microseconds of arc duration. Forexample, the scale 272 may show a range from one third millisecond to 8milliseconds.

FIG. 12 indicates how the previously described circuit in FIG. 4 may bemodified for cooperation with the cam arrangementshown in FIG. 6. Theswitch 50 is a push button switch which energizes a relay having anormally open locking contact 274 in a locking circuit that includes thepreviously mentioned switch 254 that is normally closed and is openedwhen released by the cam lobe 253. Thus momentarily depressing thestarter switch 50 long enough to permit switch 254 to close causes onerotation of the cam shaft to be carried out automatically. First the twoclamping solenoids 214 and 230 are energized and subsequently the switch51a is operated by the cam 245 to set up the required voltage across thetwo workpieces. Still later the cam contact 247 of FIG. 6 cooperateswith contact 248 to initiate the welding arc. After the heated workparts abut with each other the switch 51a is released by the cam lobe245 for recharging the capacitor bank and subsequently the energizationof the two clamping solenoids by the switch 242 is terminated. Then thecam lobe 250 closes the switch 251 momentarily to operate the ejectionsolenoid 232 to eject the welded product. Finally, cam lobe 253 opensthe switch 254 to break the relay locking circuit to operate the clutch45b and the brake 45a to stop the cam assembly.

In a typical embodiment of the invention, the motor 47 operates at18,000 r.p.m. and incorporates reduction gearing which steps down thevelocity by one sixth to rotate the shaft 46 at approximately 300 r.p.m.When the clutch 45b is closed an auxiliary mass is added to theconstantly rotating structure, which auxiliary mass includes parts ofthe clutch 45b, parts of the brake 45a, the shaft 44, the gears 42 and43 and the rotary cam means along with the shaft on which the rotary cammeans is mounted. With the major portion of the driving mass constantlyrotating at 1,800 r.p.m. and a minor portion thereof constantlyoperating at 300 r.p.m. and with the auxiliary mass thatis added by theclutch 45b and associated parts quickly accelerated to 300 r.p.m. tostart an operating cycle and with all of these rotating parts having acombined weight of approximately 2% pounds the momentum available foractuating the movable workholder 20a is approximately 48 pounds and withthe movable workholder weighing approximately 6 ounces the ratio of theavailable driving momentum to the inertia of the workholder 20a is128:1. It may be readily appreciated that the driving momentum is sooverpowering that the effect of picking up the auxiliary weightincluding the cam means is insignificant and full acceleration of thecam means is accomplished in advance of the operating cycle, i.e.,before the cam 40 starts to actuate the workholder 20a.

Whenever a change over the welding of different workpieces requires achange in the rate at which the gap between the two workpieces isclosed, it is a simple matter to substitute a new cam 40 having lobeswith slopes of different inclination.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be covered by thefollowing claims.

We claim:

l. A pulse arc welder comprising:

energy storage means for accumulating a particular amount of electricalenergy at a particular voltage;

means defining a main gap across which an arc is to be ignited;

circuit means including series impedance means for connecting the gapdefining means in series with the energy storage means, the particularvoltage when effective across the gap being insufficient to strike anarc;

a first, low voltage trigger circuit including switching means forestablishing first and second operating states in the trigger circuit,and providing a low voltage signal at least when the switching meanschanges the trigger circuit from the first to the second state;

a second, high voltage circuit responsive to the low voltage signal andconverting same into a high voltage signal;

a third, high voltage circuit including a capacitor, an inductance andan auxiliary discharge gap, an arc across the auxiliary discharge gapestablishing a closed tank circuit which includes the capacitor and theinductance;

circuit means for providing to the capacitor a high voltage, to obtain acharge of the capacitor at the high voltage, the charge dischargingoscillatorily in the tank circuit when the auxiliary gap is bridged byan are;

means to apply the high voltage signal as developed by the secondcircuit as arc ignition signal to the auxiliary discharge gap; and

means coupling the tank circuit to the impedance, so that uponoscillatory discharge of the capacitor in the tank circuit a very highvoltage is developed across the impedance to be effective across themain gap.

2. In a circuit for igniting an arc, the combination comprisa first lowvoltage circuit including a capacitor and being responsive to anexternal trigger signal to discharge the capacitor at a rapid rate;

a second high voltage circuit including a control electrode and beingresponsive to the capacitor discharge to produce a high voltage spike atsaid control electrode;

a third high voltage circuit including a resonant circuit having acapacitor, an inductance and a pair of electrodes, the resonant circuitbeing disabled when no discharge current flows between the pair ofelectrodes, the pair of electrodes being coupled to the controlelectrode so that a discharge current flows between the pair ofelectrodes when a high voltage spike is applied to the controlelectrode, causing the resonant circuit to resonate;

a fourth very high voltage circuit including a multiturn coil coupled tothe inductance of the resonant circuit to develop a very high voltage asthe resonant circuit resonates;

means defining a discharge gap serially coupled to the coil,

an arc is being struck across the gap by the very high voltage whendeveloped across the coil; and

a low voltage source coupled in series with the coil and the dischargegap for sustaining an are when struck across the discharge gap.

3. A circuit for igniting an arc across a gap at a particular instant,the combination comprising:

electrode means for defining the gap;

a saturable step-up transformer having a primary and a secondarywinding, the secondary winding being connected in series with theelectrode means;

capacitor means connected to the primary winding for defining therewitha tank circuit;

a first and a second electrode defining a second discharge gap andconnected to the capacitor means and the primary winding to close thetank circuit only upon discharge across the second gap;

first circuit means connected to the first and second electrodes forapplying different voltage potentials to the first and second electrodescausing the capacitor means to charge;

a third electrode interposed in the second gap;

second circuit means connected to the third electrode for normallymaintaining the potential of the third electrode at a level in betweenthe potentials as applied to the first and second electrodes, the first,second and third electrodes being positioned so that no arc ignitesbetween either of them as long as they are under control of the firstand third circuit means; and

third circuit means connected to the second circuit means for producingat least one high voltage spike as between the first and the secondelectrodes to ignite an arc across the second gap for causing the tankcircuit to resonate producing a high voltage across said secondarywinding for igniting an arc across the first gap.

4. A device for accurately timing the commencement of an arc dischargeacross a gap, comprising:

first means for providing a voltage insufficient to ignite an are butsufficient to sustain an are when established;

variable impedance means for coupling the first means to the gap;

means defining an auxiliary discharge gap;

a tank circuit which includes the auxiliary gap, but prevented fromoscillating when the auxiliary gap is deionized, the tank circuit beingcoupled to the variable impedance for developing a very high voltageacross the impedance means and the gap when the tank circuit resonates;and

means for igniting an arc across the auxiliary gap to cause the tankcircuit to resonate.

5. A combination for controlling the ignition of an arc;

a first and a second storage means for respectively accumulatingparticular amounts of electrical energy;

a first, high d-c voltage source connected to the first storage meansfor supplying thereto electrical energy at a high d-c voltage level;

a second, low d-c voltage source for connection to the second storagemeans for supplying thereto electrical energy at a low d-c voltage levelthereof;

a discharge path including means defining an air gap for connection tothe second storage means and for sustaining an are when ignited acrossthe air gap;

a controllable h-f circuit including the first storage means and anauxiliary discharge gap which when ionized causes the first storagemeans to discharge to produce h-f pulses, further including means tocouple the h-f pulses to the discharge path to be effective across theionized air gap as igniting signal; and

means for igniting the auxiliary discharge gap.

UNETEE fflfflfii OFFECE CERTEWCA'EE @F {IORRECTION Patent ,423 DatedApril 4, 1972 Inventor(s) Delbert L. Phillips and Lewis Clark FeightnerIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Assiqnee of recorfi for this Patent is as follows:

NEW TWIST CONNECTOR CORPORATION Santa Monica, California a Californiacorporation Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. ca MRSELALL DANN Arresting Officer Commissioner ofPatents :ORM 904050 uscoMM-Dc 60376-P69 U.S GOVERNMENT PR1NY|NG OFFICEZQ69 0-355-334 UNETEE EFTATEW EQPJEENT @FFECE CERTEFEQATE @F QRECTIONPatent No. 3,654,423 Dated 7 April 4, 1972 Inventor(s) Delbert L.Phillips and Lewis Clark Feightner It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Assignee of record for this ?atent is as follows:

NEW TWIST CONNECTOR CORPORATION Santa Monica, California a Californiacorporation Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. Cn I L' \SHALL DANN Attesting Officer Commissionerof Patents USCOMM-DC 60376-P69 t: u s GOVERNMENT PRINTING OFFICE: I969o-ass-aaa FORM 04050 (10-69)

1. A pulse arc welder comprising: energy storage means for accumulating a particular amount of electrical energy at a particular voltage; means defining a main gap across which an arc is to be ignited; circuit means including series impedance means for connecting the gap defining means in series with the energy storage means, the particular voltage when effective across the gap being insufficient to strike an arc; a first, low voltage trigger circuit including switching means for establishing first and second operating states in the trigger circuit, and providing a low voltage signal at least when the switching means changes the trigger circuit from the first to the second state; a second, high voltage circuit responsive to the low voltage signal and converting same into a high voltage signal; a third, high voltage circuit including a capacitor, an inductance and an auxiliary discharge gap, an arc across the auxiliary discharge gap establishing a closed tank circuit which includes the capacitor and the inductance; circuit means for providing to the capacitor a high voltage, to obtain a charge of the capacitor at the high voltage, the charge discharging oscillatorily in the tank circuit when the auxiliary gap is bridged by an arc; means to apply the high voltage signal as developed by the second circuit as arc ignition signal to the auxiliary discharge gap; and means coupling the tank circuit to the impedance, so that upon oscillatory discharge of the capacitor in the tank circuit a very high voltage is developed across the impedance to be effective across the main gap.
 2. In a circuit for igniting an arc, the combination comprising: a first low voltage circuit including a capacitor and being responsive to an external trigger signal to discharge the capacitor at a rapid rate; a second high voltage circuit including a control electrode and being responsive to the capacitor discharge to produce a high voltage spike at said control electrode; a third high voltage circuit including a resonant circuit having a capacitor, an inductance and a pair of electrodes, the resonant circuit being disabled when no discharge current flows between the pair of electrodes, the pair of electrodes being coupled to the control electrode so that a discharge current flows between the pair of electrodes when a high voltage spike is applied to the control electRode, causing the resonant circuit to resonate; a fourth very high voltage circuit including a multiturn coil coupled to the inductance of the resonant circuit to develop a very high voltage as the resonant circuit resonates; means defining a discharge gap serially coupled to the coil, an arc is being struck across the gap by the very high voltage when developed across the coil; and a low voltage source coupled in series with the coil and the discharge gap for sustaining an arc when struck across the discharge gap.
 3. A circuit for igniting an arc across a gap at a particular instant, the combination comprising: electrode means for defining the gap; a saturable step-up transformer having a primary and a secondary winding, the secondary winding being connected in series with the electrode means; capacitor means connected to the primary winding for defining therewith a tank circuit; a first and a second electrode defining a second discharge gap and connected to the capacitor means and the primary winding to close the tank circuit only upon discharge across the second gap; first circuit means connected to the first and second electrodes for applying different voltage potentials to the first and second electrodes causing the capacitor means to charge; a third electrode interposed in the second gap; second circuit means connected to the third electrode for normally maintaining the potential of the third electrode at a level in between the potentials as applied to the first and second electrodes, the first, second and third electrodes being positioned so that no arc ignites between either of them as long as they are under control of the first and third circuit means; and third circuit means connected to the second circuit means for producing at least one high voltage spike as between the first and the second electrodes to ignite an arc across the second gap for causing the tank circuit to resonate producing a high voltage across said secondary winding for igniting an arc across the first gap.
 4. A device for accurately timing the commencement of an arc discharge across a gap, comprising: first means for providing a voltage insufficient to ignite an arc but sufficient to sustain an arc when established; variable impedance means for coupling the first means to the gap; means defining an auxiliary discharge gap; a tank circuit which includes the auxiliary gap, but prevented from oscillating when the auxiliary gap is deionized, the tank circuit being coupled to the variable impedance for developing a very high voltage across the impedance means and the gap when the tank circuit resonates; and means for igniting an arc across the auxiliary gap to cause the tank circuit to resonate.
 5. A combination for controlling the ignition of an arc; a first and a second storage means for respectively accumulating particular amounts of electrical energy; a first, high d-c voltage source connected to the first storage means for supplying thereto electrical energy at a high d-c voltage level; a second, low d-c voltage source for connection to the second storage means for supplying thereto electrical energy at a low d-c voltage level thereof; a discharge path including means defining an air gap for connection to the second storage means and for sustaining an arc when ignited across the air gap; a controllable h-f circuit including the first storage means and an auxiliary discharge gap which when ionized causes the first storage means to discharge to produce h-f pulses, further including means to couple the h-f pulses to the discharge path to be effective across the ionized air gap as igniting signal; and means for igniting the auxiliary discharge gap. 